DarkSide-20k and the future Liquid Argon Dark Matter program

Giuliana Fiorillo Università degli Studi di Napoli “Federico II” & INFN Napoli

UCLA DM Conference Los Angeles February 23, 2018

The case for DarkSide-20k

• WIMPs are still excellent candidates for particle dark matter

• WIMP masses: 0.01 - 10 TeV and cross sections: 10-40 - 10-50 cm2

• Several 100 ton yr exposures needed for a discovery program

➡ staged program to reach fully scalable detector design and operation at the multi-ton scale

2

The DarkSide program at LNGS

DarkSide-10

technical prototype no DM goal

DarkSide-50 DarkSide-20k

sensitivity 10-47 cm2

sensitivity 10-44 cm2

2011 2012 2013 2014 2016 2018 2019 2020 202120172015 2022

A scalable technology for direct WIMP search: 2-phase low background Argon TPC

2−10 1−10 1 10]2WIMP mass [TeV/c

50−10

49−10

48−10

47−10

46−10

45−10

44−10

43−10

42−10

41−10]2 [cm

SI

σWIMP-nucleon

DarkSide-20k

(100 t yr p

roj.)

DarkSide-20k

(200 t yr p

roj.)

Future 300-t

onne GADMC D

etector (1kt

yr proj.)

DEAP-3600 (p

roj.)

LUX (2017)

LZ (proj.)

PANDAX-II

(2017)

XENON1T (2

017)

XENON1T (p

roj.)

XENONnT (p

roj.)

WARP (2007)

DarkSide-5

0 (2015)

DEAP-3600 (2

017)

Future 300-t

onne GADMC d

etector (3kt

yr proj.)

DarkSide-50 (201

8)

Neutrino f

loor

4

DarkSide design: how to defeat background

‣ Identification: • ER/NR discrimination using PSD• ER/NR discrimination via S2/S1• 3D reconstruction of interactions

(rejects γ and surface bkgs)

‣Passive suppression: • Isotopically depleted Argon• Low radioactive materials• Low radioactive light-detectors

‣Active shielding: • Neutron Veto (Liquid Scintillator)• Muon Veto (Water Cherenkov Detector)

5

DarkSide-50

6

✓ ER/NR Discrimination

• PSD vs S1 for 1422 kg d atmospheric argon (AAr) exposure

• 1.5x107 ER events from 39Ar activity in AAr and Zero NR events

✓ Suppression: AAr Vs UAr

• Underground argon (UAr): 150 kg successfully extracted from a CO2 well in Colorado

• 39Ar depletion factor >1400

39Ar in UAr < 1 mBq/kg

PRD

, 93

(201

6): 0

8110

1(R

)

S1 [PE]50 100 150 200 250 300 350 400 450

90

f

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0

5000

10000

15000

20000

25000

50% 65% 80% 90% 95% 99%

]nr

Energy [keV20 40 60 80 100 120 140 160 180 200

PLB

743,

456

(201

5)

see talk by P. Meyers

Scaling up towards the neutrino floor:next stage world Argon program

7

• DarkSide • DEAP-3600• miniCLEAN• ArDM

> 350 researchers from 80 Institutes➠ Global Argon Dark Matter Collaboration

(GADMC)

DarkSide-20k ⇢ multi 100 ton

DS50-1: discrimination 1.5 107 at LY=7 PE/keV at 200 V/cm [PLB 743, 456 (2015)]DEAP-1: predict discrimination 1010 at LY=8 PE/keV [Astropart. Phys. 85, 1 (2016)]

LAr high discrimination power + depleted argon allow for the several hundreds ton yr background-free exposures needed to reach the neutrino floor

see talk by S. Westerdale

DarkSide future program

8

DarkSide-20k a 20-tonnes fiducial argon

detector100 tonne×year background-free

search for dark matter

GADMC detector a 300-tonnes depleted argon

detector1,000 tonne×year background-free

search for dark matter

20- 16171819202122232425262728293031323334DS-20kGADMC

DarkSide-20k

9

arXiv:1707.08145100 ton yr background-free exposure

Conceptual approach: ultra-low background levels and the ability to measure backgrounds in situ

Baseline design:

• 30 ton total, 20 ton fiducial, underground argon

• 14m2 SiPM sensors (low radioactivity, increased LY)

• inside high efficiency neutron shield/veto

Two key technologiesenabling DarkSide-20k and future LAr program

• Cryogenic SiPMs • DarkSide-20k @ Abruzzo large area,

cryogenic silicon photomultiplier optical modules assembly and test facility (Nuova Officina Assergi - NOA)

• Liquid argon target depleted in the radioactive 39Ar

• URANIA extraction of large quantities of underground argon

• ARIA Isotopic separation via cryogenic distillation

10

• Big cryogenic distillation column in Seruci, Sardinia

• Final chemical purification of the UAr

• Can process O(1 tonne/day) with 103 reduction of all chemical impurities

• Ultimate goal is to isotopically separate 39Ar from 40Ar

URANIA• Procurement of 50 tonnes of UAr from same

Colorado source as for DS-50

• Extraction of 100 kg/day, with 99.9% purity

• UAr transported to Sardinia for final chemical purification at Aria

11

ARIA

see talk by A. Renshaw

Nuova Officina Assergi

• SiPM cryotest

• Tile & FEB packaging

• Photon Detector Modules and Motherboards (25 PDM) assembly

see talk by A. Razeto

Tile FEB PDM

MB

]nr

Energy [keV0 10 20 30 40 50 60 70 80

NR Acceptance

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

200f

150f

120f

90f

S1 [PE]50 100 150 200 250 300 350 400 450

200

f

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

1

10

210

310

410

]ee

Energy [keV5 10 15 20 25 30 35 40 45 50

0.001 evts/1 PE leakage

DarkSide-20k PSD

13

f200: fraction of S1 light in 200ns

39Ar

projected LY: 10PE/keV

arXiv:1707.08145

]nr

Energy [keV0 10 20 30 40 50 60 70 80

NR Acceptance

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

200f

150f

120f

90f

S1 [PE]50 100 150 200 250 300 350 400 450

200

f

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

1

10

210

310

410

]ee

Energy [keV5 10 15 20 25 30 35 40 45 50

0.001 evts/1 PE leakage

DarkSide-20k PSD

13

S1 [PE]50 100 150 200 250 300 350 400 450

200

f

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

1

10

210

310

]nr

Energy [keV20 40 60 80 100 120 140 160 180

90% NR acceptance

f200: fraction of S1 light in 200ns

nuclear recoils

39Ar

projected LY: 10PE/keV

• NR acceptance region defined by requiring < 0.005 ER events/(5-PE bin) (< 0.1 events in the WIMP search region),

• The resulting equivalent ER reduction factor is > 3 × 109 , more than sufficient to maintain background-free operation for more than 200 t yr.

arXiv:1707.08145

• TPC inside a SS cryostat, inside a liquid scintillator active neutron veto, inside a 15m diameter 16m tall water tank, as active muon veto

➡ assuming the same level of radioactivity as in DS50, ER background dominated by 39Ar

➡ (α ,n) reactions in PTFE reflector and cryostat largest sources of neutrons

14

arXi

v:17

07.0

8145

DarkSide-20k backgrounds

A LAr shield for DarkSide-20k

• AAr in ProtoDune style large cryostat to provide shielding and active VETO

• allows to eliminate Liquid Scintillator Veto and Water tank

➡Significantly simplify the overall system complexity and operation

➡Fully scalable design for future larger size detector (300 ton)

15

CERN Neutrino Platform: • Two almost identical

cryostats built for NP02 and NP04 experiments

• About 8x8x8 m3 inner volume, 750 t of LAr in each one

• Cryostat technology and expertise taken from LNG industry

• Construction time: 55 weeks (NP04), 37 weeks (NP02)

• Thought since the beginning to be installable underground

DarkSide-20k inner detector

• AAr shield provides the opportunity to remove the largest contribution to neutron background, the SS cryostat:

• CU vessel with the shape of the TPC (octagonal prism) providing also a possible path to increase the active Argon size

• TPC reflector realised from a sandwich of acrylic+3M foil removes the second big contributor to neutron background (PTFE)

➡Residual neutron background from sub-leading contribution from substrates, electronic components, optical fibers, copper parts and acrylic

DarkSide-20k nVeto conceptual design

• Several options are being considered for a cryogenic veto inside the LAr shield: • hydrogenated materials for

efficient thermalisation • possible addition of further

material with high capture cross section

➡ no showstoppers for meeting the goal of 0.1 neturon/100 t yr identified so far, considering also the reduced neutron background of the new design

2−10 1−10 1 10]2WIMP mass [TeV/c

50−10

49−10

48−10

47−10

46−10

45−10

44−10

43−10

42−10

41−10]2 [cm

SI

σWIMP-nucleon

DarkSide-20k

(100 t yr p

roj.)

DarkSide-20k

(200 t yr p

roj.)

Future 300-t

onne GADMC D

etector (1kt

yr proj.)

DEAP-3600 (p

roj.)

LUX (2017)

LZ (proj.)

PANDAX-II

(2017)

XENON1T (2

017)

XENON1T (p

roj.)

XENONnT (p

roj.)

WARP (2007)

DarkSide-5

0 (2015)

DEAP-3600 (2

017)

Future 300-t

onne GADMC d

etector (3kt

yr proj.)

DarkSide-50 (201

8)

Neutrino f

loor

DarkSide-20k sensitivity

19

Conclusions• DarkSide-20k set to start in 2021, with a projected

sensitivity of 1×10-47 cm2 for a 1 TeV/c2 dark matter particle mass and an exposure of 100 tonne×yr

• Global Argon Dark Matter Collaboration aiming at 1,000 tonne×year search for dark matter

• Two key enabling technologies:

‣ Upgrade of production of depleted argon to many tonnes (URANIA & ARIA)

‣ Cryogenic photosensors based on SiPM arrays with area of 15 m2 (NOA)

20

DarkSide-20k @ LNGS Hall C

THANK YOU

1ton prototype TPC

15PDMseach

25PDMseach

TriangularMotherBoard(TRB)

SquareMotherBoard(SQB)